Chlorinated lithium manganese oxide spinel cathode material with charge transfer catalyst coating, method of preparing the same, and Li electrochemical cell containing the same

Abstract

A process for preparing a stable li_xMn_2-yMe_yO_4-zCl_z material with a mo_b or MMn_aO_b charge transfer catalyst coating is provided, where Me is Fe, Co, or Ni and M is Bi, As, or Sb. In addition, a li_xMn_2-yMe_yO_4-zCl_z material with a mo_b or MMn_aO_b charge transfer catalyst coating is provided. Furthermore, a lithium or lithium ion rechargeable electrochemical cell is provided, which includes a cathode material (in a positive electrode) containing a li_xMn_2-yMe_yO_4-zCl_z material with a mo_b or MMn_aO_b charge transfer catalyst coating.

Description

GOVERNMENT INTEREST

The invention described herein may be manufactured, used, imported, sold, and licensed by or for the Government of the United States of America without the payment of any royalty thereon or therefor.

FIELD OF THE INVENTION

The present disclosure relates generally to the field of electrochemical power sources and, more particularly, to rechargeable lithium and lithium-ion batteries using manganese-based materials as a positive electrode.

BACKGROUND OF THE INVENTION

Perhaps the most popular battery chemistries that have hit the consumer market recently are lithium-based systems. Lithium batteries use high valence metal oxide materials, which are reduced during the electrochemical reaction. This reaction in rechargeable lithium and rechargeable lithium ion batteries must be fully reversible in order to have a commercially viable cell. These electrochemical systems include manganese-based lithium metal oxides configured in lithium, lithium ion, and lithium polymer electrochemical cells. Common reversible metal oxide materials used in lithium batteries include Li_xMn₂O₄, Li_xMnO₂, Li_xCoO₂, Li_xNiO₂, and Li_xNi_yCo_zO₂.

Today, rechargeable lithium batteries are used in portable electronic devices including cellular phones and laptop computers. Future use of rechargeable lithium battery systems is targeted at applications related to electronic vehicles and pairing with fuel cells to produce high-energy systems with excellent pulse capabilities. Lithium batteries have the flexibility of being packaged into either cylindrical or prismatic cell designs; this feature makes them applicable to almost any portable electronic system where battery volume is a concern.

The benefits of lithium battery systems include high specific energy (Wh/kg) and high energy density (Wh/l). Lithium electrochemical systems produce a relatively high nominal voltage between 3.0 and 4.75 volts. Lithium electrochemical systems can operate between 3.0 and 4.35 volts or between 2.0 and 3.5 volts. Additionally, lithium electrochemical systems have excellent charge retention due to a low self-discharge rate.

Manganese dioxide (MnO₂) based materials are attractive for use as a cathode material in lithium electrochemical systems. MnO₂ is attractive because of its high energy density and low material cost. MnO₂ is an active material which creates a skeletal structure that allows lithium cations to fill vacancies and voids within the structure. Ideally, this structure does not change with cycling; altering of this crystal structure may cause capacity fading. Additionally, the MnO₂ active material exists in different forms. These forms include a lithiated spinel (Li_xMn₂O₄) and its different structures denoted by α, β, γ, and λ. In lithium electrochemical cells, the active material is bound to an aluminum current collector with either polytetrafluoroethylene (commercially available under the trade name TEFLON, manufactured by DuPont) or polyvinylidene fluoride mixed with conductive carbon. The conductive carbon serves as an aid for electron transfer.

Capacity fading is a major problem for rechargeable lithium cells. Capacity fading is the loss of cycle capacity in a cell over the life of an electrochemical system, limiting the practical number of cycles that may be used. In lithium battery systems, capacity fading is often attributed to the degradation of the active cathode material. This cyclic capacity loss is a result of both changes in composition and crystal structure of the active cathode material. Additionally, throughout the life of a cell, parasitic side reactions occur between chemical species of all cell components. Methods of reducing this effect include modifying the crystal structure and/or composition of the active material.

Capacity fading associated with the cathode material has also been linked to the fracture of active material and the dissociation or disconnection of the fractured active material from the electrode. Fractures are caused by mechanical stress-strain of MnO₂ crystal structures during cycling of the cell. Stress-strain forces act on the crystal structures as a result of repeated phase transitions. These stress-strain forces are due to the insertion and extraction of lithium in the cathode lattice. This frequent conversion in geometry and dimension of the crystal lattice creates a significant mechanical strain on the cathode. This mechanical strain is believed to electrically disconnect active material from the electrode through fracture. Additionally, an external influence, such as elevated temperature, can also promote cathode fracture. In this case, structural vibrations increase with temperature, resulting in the disconnection of the fractured active material from the electrode.

Another major cause of capacity fading in manganese-based cathodes is the dissolution of manganese into the electrolyte. Through a series of chemical reactions, manganese (Mn²⁺) is removed from the cathode and dissolved into the electrolyte, resulting in a decrease of active material in the cathode. Manganese dissolution is linked to reactions with the electrolyte and, more importantly, the impurities dissolved within the electrolyte. Many of these reactions are linked to the water content of the electrolyte and the presence of hydrofluoric acid (HF). The products of parasitic reactions are phase transitions of the MnO₂ structure, which results in the formation of Mn₂O₃ and Mn₃O₄.

Manganese dioxide (MnO₂) provides a skeletal background for lithium intercalation during cycling of a lithium electrochemical cell. When fully charged, manganese particles have a meta-stable 4+ valence state. This meta-stable 4+ valence state allows for the attraction and intercalation of lithium cations into the lattice structure. As lithium cations fill the skeleton crystal structure during discharge, the crystal structure of the active material changes. Charging of the cell removes these lithium cations from the cathode, again altering the crystal structure. Ideally, this is a completely efficient and reversible process, but realistically, continuous crystal structure changes lead to phase transitions that can impede lithium mobility. As a result of these phase changes, unwanted crystal structures develop that are either too stable for electrochemical reactions or block the insertion/extraction paths of lithium cations into the cathode material. This general phenomenon is regarded as the major contributor to capacity fading.

MnO₂ exists in several phases or crystal structures and are referred to by the following prefixes: α, β, γ, and λ. α-MnO₂ is the most stable MnO₂ structure. α-MnO₂ is one-dimensional and the lattice contains both one by one and two by two channels for lithium insertion/extraction. β-MnO₂ is a tetragonal structure with the lattice containing one by one channels for lithium insertion/extraction. γ-MnO₂ is also one-dimensional, existing in both hexagonal and orthorhombic crystal structures with a lattice that contains one by two channels for lithium insertion/extraction. Because of their stability α-MnO₂, β-MnO₂, and γ-MnO₂ are not considered rechargeable. However, cycling of lithium into the α-MnO₂, β-MnO₂, and γ-MnO₂ lattice can be achieved with rigid stoichiometric control.

λ-MnO₂ is the conventional form of MnO₂ based cathode material for rechargeable lithium electrochemical systems. λ-MnO₂ is created through the delithiation of Li_xMn₂O₄ AB₂O₄ spinel. The λ-MnO₂ crystal structure is maintained through both charge and discharge of the LiMn₂O₄ spinel. The maintenance of the λ-MnO₂ structure during insertion and extraction of lithium in the Li_xMn₂O₄ spinel makes it an attractive couple with lithium for rechargeable electrochemical systems. The λ-MnO₂ crystal structure is a three dimensional cubic array. This crystal structure promotes mechanical stability and adequate pathways for lithium insertion/extraction. Degradation of the λ-MnO₂ crystal structure, forming α, β, or γ-MnO₂ crystals and other Mn_xO_y phases, reduces the capacity of the cathode material.

As lithium intercalates, the size and orientation of the crystal structures change. In Li_xMn₂O₄ spinel materials, when 0.05<x<1, the crystal structure is cubic (λ-MnO₂). When 1<x<1.8, the structure of Li_xMn₂O₄ (no longer a AB₂O₄ spinel) is tetragonal. Additionally, when x<0.05, a phase transition to the more stable α, β, and γ MnO₂ can occur. Continued charge and discharge promotes the transformation of the cubic crystal structure to other cubic, tetragonal, and monoclinic phases. Tetragonal and monoclinic crystal structures may become inactive, leading to the loss of active cathode material.

Voltage control, maintaining 0.05<x<1, allows for the mitigation of the formation of unwanted crystal structures. When the potential of the lithium/Li_xMn₂O₄ electrochemical system is maintained between 3.0 and 4.25 volts, the cubic phase is maintained. Once the potential of the system drops below 3.0 volts, the Li_xMn₂O₄ cathode material undergoes a phase change from cubic to tetragonal. When the potential of the system increases above 4.25 volts, the Li_xMn₂O₄ cathode material becomes stripped of the lithium component and undergoes a phase change from cubic (λ-MnO₂) to the more stable α, β and/or γ MnO₂.

Other phase transitions that lead to capacity fading include the formation of Mn₂O₃ and Mn₃O₄. The Mn₂O₃ and Mn₃O₄ formations result from the liberation of oxygen in the MnO₂ and Mn₂O₄ structures. The valence state of manganese in these structures is 3+ or less. This lower valence state creates a stable crystal structure that is not conducive to lithium intercalation and, therefore, not rechargeable. As more Mn₂O₃ and Mn₃O₄ are formed, less MnO₂ and Mn₂O₄ remain and the usefulness of the cathode decreases.

Thus, one of the disadvantages of conventional lithium manganese-based AB₂O₄ spinel materials is the limited cycle life and limited rate capability for lithium electrochemical systems. Furthermore, this problem is a major obstacle for rechargeable lithium battery technology. An additional limiting factor for lithium manganese-based AB₂O₄ spinel materials is the time required to process the raw materials and synthesize the desired product; conventional methods require multiple mixing, grinding and calcining steps, which take days to complete.

SUMMARY OF THE INVENTION

The present disclosure resolves the aforementioned problems with rate capability associated with conventional lithium manganese-based AB₂O₄ spinel cathode materials in lithium electrochemical systems and rechargeable lithium electrochemical systems. More specifically, the present “O” site and “B” site modified lithium manganese-based AB₂O₄ spinel cathode material, which has a surface charge transfer catalyst coating, exhibits improved rate capability and under-voltage tolerance and high rate durability, avoiding problems associated with loss of reversibility in lithium batteries without suffering from the disadvantages, limitations, and shortcomings associated with rigid current limits and rigid stoichiometry control. “O” site modification describes substituting an alternative element on the “O” site of the AB₂O₄ spinel; likewise “B” site modification describes an alternative element substitution for the “B” site of the AB₂O₄ spinel. These benefits are also demonstrated in the “B” and “O” site modified AB₂O₄ spinel cathode material with the surface charge transfer catalyst coating. In addition, the presently disclosed cathode materials meet other significant lithium battery operational objectives (e.g., low impedance and thermal stability).

In addition, the cycle life of the lithium cells fabricated using the present spinel material is significantly longer than cells fabricated using conventional lithium manganese-based AB₂O₄ spinel materials. The charge transfer catalyst coated and chlorine-modified Li_xMn₂O_4-zCl_z or Li_xMn_2-yMe_yO_4-zCl_z cathode material allows for over-discharge protection. Reversibility in the material is maintained after cell potential excursions less than 2.0 volts are performed. When the charge transfer catalyst coated and chlorine-modified Li_xMn₂O_4-zCl_z or Li_xMn_2-yMe_yO_4-zCl_z cathode material is coupled with a lithium anode, it successfully cycles between 4.5 and 2.0 volts without significant degradation. In contrast, conventional Li_xMn₂O₄ cathode materials tend to degrade as a result of stress/strain-induced material fracture and formation of Mn₂O₃ and Mn₃O₄. Furthermore, the relatively low temperatures of the preparation method according to the present disclosure afford better process control, and the fabrication time of the present disclosure is significantly lower than that of the conventional lithium manganese-based AB₂O₄ spinel materials.

In one embodiment, a method of preparing a charge transfer catalyst coated homogeneously dispersed “O” site modified lithium manganese-based AB₂O₄ spinel cathode material includes mixing a lithium source, a chlorine source, and a manganese source to form a first mixture. The first mixture is calcined to produce a homogeneously dispersed “O” site modified lithium manganese-based AB₂O₄ spinel cathode material. Then, the homogeneously dispersed “O” site modified lithium manganese-based AB₂O₄ spinel cathode material, a charge transfer catalyst salt, and a chelating agent are mixed to produce a second mixture. The second mixture is heated to produce a gel, and the gel is ignited to form an ash. The ash is calcined to produce a homogeneously dispersed “O” site modified lithium manganese-based AB₂O₄ spinel cathode material including a charge transfer catalyst coating. The charge transfer catalyst coating contains MO_b and/or MMn_aO_b, and M is bismuth, arsenic, or antimony. According to another aspect of the present disclosure, a method of preparing a charge transfer catalyst coated homogeneously dispersed “O” site and “B” site modified lithium manganese-based AB₂O₄ spinel cathode material is provided.

In another embodiment, a homogeneously dispersed, chlorine-modified lithium manganese-based AB₂O₄ spinel cathode material including Li_xMn_2-yMe_yO_4-zCl_z and a charge transfer catalyst coating is described. The charge transfer catalyst coating contains MO_b and/or MMn_aO_b; Me is iron, cobalt, or nickel; and M is bismuth, arsenic, or antimony. In this embodiment, the Li_xMn_2-yMe_yO_4-zCl_z is O-site modified. In another aspect of the present disclosure, the charge transfer catalyst coated Li_xMn_2-yMe_yO_4-zCl_z is “O” site and “B” site modified.

In yet another embodiment, the present disclosure provides a lithium electrochemical cell that includes an anode and a cathode including the present charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material. In another aspect of the present disclosure, an electrochemical cell is described that includes an anode and a cathode including the present charge transfer catalyst coated “O” site and “B” site modified lithium manganese-based AB₂O₄ spinel cathode material.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide further understanding of the present disclosure, and are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the present disclosure, and together with the description serve to explain the principles of the present disclosure. The present disclosure will now be described further with reference to the accompanying drawings as follows:

FIG. 1 is a flowchart illustrating process steps in an exemplary embodiment of the present disclosure, which yields a charge transfer catalyst coated chlorine “O” site modified AB₂O₄ spinel material.

FIG. 2 is a flowchart illustrating process steps in an exemplary embodiment of the present disclosure, which yields a charge transfer catalyst coated “B” and “O” site modified AB₂O₄ spinel material.

FIG. 3 is a graph showing x-ray diffraction data for an exemplary formulation mixture according to exemplary embodiments of the present disclosure compared to an undoped spinel material used as a reference standard.

FIG. 4 is a graph showing x-ray diffraction data for a narrow region for an exemplary formulation mixture according to exemplary embodiments of the present disclosure, compared to LiMn₂O₄ and Bi₂Mn₄O₁₀ as reference standards.

FIG. 5 is a graph showing x-ray fluorescence data for an exemplary formulation mixture according to exemplary embodiments of the present disclosure, compared to Si, P, S, Bi, Cl, Pd, and Mn as reference standards.

FIG. 6 is a graph showing x-ray fluorescence data for an exemplary formulation mixture according to exemplary embodiments of the present disclosure, compared to Si, P, S, Bi, Cl, Pd, and Mn as reference standards.

FIG. 7 is a graph showing thermogravimetric analysis results for an exemplary formulation mixture according to exemplary embodiments of the present disclosure.

FIG. 8 is a backscattered scanning electron microscope (SEM) image of the particles of an exemplary formulation mixture according to exemplary embodiments of the present disclosure.

FIG. 9 is a graph illustrating specific discharge capacity over 500 cycles for a lithium cell containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

FIG. 10 is a graph showing discharge capacity over 600 cycles for a lithium cell containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

FIG. 11 is a graph illustrating the charge and discharge curves for cycles 25, 505, and 565 for a lithium cell containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

FIG. 12 is a graph showing discharge capacity to 225 cycles comparing two lithium cells, one containing a Li_xMn₂O₄ spinel and another containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

FIG. 13 is a graph of differential capacity comparing three lithium cells, one containing a Li_xMn₂O₄ spinel, another containing an “O” site modified lithium manganese-based AB₂O₄ spinel cathode material, and a third containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

FIG. 14 is a bar graph illustrating the percent of original discharge capacity at cycle 150 versus cycle 5 for five different lithium cells, one containing an “O” site modified lithium manganese-based AB₂O₄ spinel cathode material, one containing Li_xMn_2-yMe_yO_4-zCl_z, where Me is Fe, Co, or Ni, with X mol % MO_b or MMn_aO_b coating cathode material according to an exemplary embodiment of the present disclosure, and the other three containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

FIG. 15 is a bar graph illustrating the percent of original discharge capacity at cycle 140 versus cycle 5 for four different lithium cells, each containing varying mole percentages of the MO_b or MMn_aO_b coating.

FIG. 16 is a graph showing the discharge capacity over 150 cycles for three lithium cells of the same chemistry containing Li_xMn_2-yMe_yO_4-zCl_z, where Me is Fe, Co, or Ni, with X mol % MO_b or MMn_aO_b coating cathode material according to an exemplary embodiment of the present disclosure.

FIG. 17 is a graph illustrating the charge/discharge curve comparison between cycle 5 and cycle 145 for lithium cell 1 containing Li_xMn_2-yMe_yO_4-zCl_z, where Me is Fe, Co, or Ni, with X mol % MO_b or MMn_aO_b coating cathode material according to an exemplary embodiment of the present disclosure.

FIG. 18 is a graph illustrating the charge/discharge curve comparison between cycle 5 and cycle 145 for lithium cell 2 containing Li_xMn_2-yMe_yO_4-zCl_z, where Me is Fe, Co, or Ni, with X mol % MO_b or MMn_aO_b coating cathode material according to an exemplary embodiment of the present disclosure.

FIG. 19 is a graph illustrating the charge/discharge curve comparison between cycle 5 and cycle 145 for lithium cell 3 containing Li_xMn_2-yMe_yO_4-zCl_z, where Me is Fe, Co, or Ni, with X mol % MO_b or MMn_aO_b coating cathode material according to an exemplary embodiment of the present disclosure.

FIG. 20 is a graph illustrating the charge/discharge curve comparison between cycle 5 and cycle 220 for lithium cell 4 containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

FIG. 21 is a graph illustrating the charge/discharge curve comparison between cycle 5 and cycle 220 for lithium cell 5 containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

FIG. 22 is a graph illustrating the charge/discharge curve comparison between cycle 5 and cycle 220 for lithium cell 6 containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

FIG. 23 is a graph illustrating the discharge curve comparison between cycle 5 and cycle 155 for a lithium cell containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

FIG. 24 is a graph illustrating the discharge/charge/discharge curve for cycle 152 and cycle 153 for a lithium cell containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

FIG. 25 is a graph showing the comparison of hysteresis upon charge and discharge of two lithium cells, one containing an “O” site modified lithium manganese-based AB₂O₄ spinel cathode material, and another containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

FIG. 26 is a graph showing the comparison of electrochemical impedance spectroscopy (EIS) of two lithium cells, one containing an “O” site modified lithium manganese-based AB₂O₄ spinel cathode material, and another containing a charge transfer catalyst coated “O” site modified lithium manganese-based AB₂O₄ spinel cathode material according to an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is a flowchart illustrating process steps in an exemplary embodiment of the present disclosure. More specifically, FIG. 1 shows exemplary steps according to the present disclosure for the preparation of Li_xMn₂O_4-zCl_z, with X mol % MO_b, or MMn_aO_b coating where M is a charge transfer catalyst metal Bi, As, or Sb via a method comprising an initial solid state milling and calcining process followed by a nitrate flame process with a calcining reaction to add the charge transfer catalyst coating. In Step S11, manganese oxide, lithium perchlorate, and lithium carbonate are mixed together and ground in Step S12. Lithium hydroxide, lithium oxide, or lithium peroxide may be substituted for lithium carbonate. This mixture is then calcined in Step S13 in a furnace at 600° C. for 2 hours. Alternatively, suitable calcination temperatures and times range from 350° C. to 800° C. (for 1 to 4 hours), from 400° C. to 600° C. (for 1.5 to 3 hours), or from 500° C. to 600° C. (for 2 to 2.5 hours). The resulting “O” site modified Li_xMn₂O_4-zCl_z yields material with x ranging from 0.05 to 1.9, 0.8 to 1.3, or 0.9 to 1.1; and z ranging from 0.005 to 0.25, 0.005 to 0.05, or 0.015 to 0.035.

In Step S14 of FIG. 1, the charge transfer catalyst salts and a chelating agent are dissolved in distilled or deionized water and nitric acid, and this solution is added to the calcined mixture. Suitable charge transfer catalyst salts include, but are not limited to, bismuth nitrate, arsenic nitrate, and antimony nitrate. Suitable chelating agents include, but are not limited to, glycine, cellulose, citric acid, a cellulose-citric acid mixture, and urea. Suitable volumetric quantities of nitric acid range from 5 vol % to 20 vol % in distilled or deionized water. In Step S15, the resultant mixture is heated to create a gel. Heating may be accomplished using a hot plate. In Step S16, the gel is heated further until auto ignition occurs. The resultant ash is ground and calcined in a furnace at 600° C. for 2 hours in Steps S17 and S18, respectively. Grinding may be accomplished using a mortar and pestle or any other conventional grinding methods. Suitable alternative calcination temperatures and times range from 350° C. to 800° C. (for 1 to 4 hours), from 400° C. to 600° C. (for 1.5 to 3 hours), or from 500° C. to 600° C. (for 2 to 2.5 hours). In the MO_b or MMn_aO_b coating, X ranges from 0.5 to 25, 1 to 20, or 3 to 15. In the final “O” site modified Li_xMn₂O_4-zCl_z material with the MO_b or MMn_aO_b coating, x ranges from 0.05 to 1.9, 0.8 to 1.3, or 0.9 to 1.1. In addition, z ranges from 0.005 to 0.25, 0.005 to 0.05, or 0.015 to 0.035. Also, a ranges from 0 to 10. Moreover, b ranges from 0 to 22, or b is greater than 0 but less than or equal to 22.

FIG. 2 is a flowchart illustrating process steps in an exemplary embodiment of the present disclosure. More specifically, FIG. 2 shows exemplary steps according to the present disclosure for the preparation of Li_xMn₂O_4-zCl_z or Li_xMn_2-yMe_yO_4-zCl_z, where Me is Fe, Co, or Ni, with X mol % MO_b or MMn_aO_b coating, where M is a charge transfer catalyst metal Bi, As, or Sb, via a method comprising an initial Li_xMn_2-yMe_yO_4-zCl_z formulation and calcining process, followed by a nitrate flame process with a calcining reaction to add the charge transfer catalyst coating.

In Step S21, a lithium source, a manganese source, a metal source (where the metal is Fe, Co, or Ni), and a chlorine source are mixed together and ground in Step S22. This mixture is then calcined in Step S23 in a furnace for 600° C. for 2 hours. Alternatively, suitable calcination temperatures and times range from 350° C. to 800° C. (for 1 to 4 hours), from 400° C. to 600° C. (for 1.5 to 3 hours), or from 500° C. to 600° C. (for 2 to 2.5 hours). This process is followed by a nitrate flame process with a calcining reaction to add the charge transfer catalyst coating (Steps 24-28).

In one embodiment, suitable lithium sources include, but are not limited to, lithium carbonate, lithium hydroxide, lithium oxide, lithium peroxide, and lithium nitrate. The manganese source and the metal source may be derived from a single source, which is a metal oxide such as (MnMe_f)O₂, (MnMe_f)₂O₃, (MnMe_f)₃O₄, or (MnMe_f)O, where Me is Fe, Co, or Ni, and the Mn to Me ratio is 1 to 0.0-0.43. For example, the metal oxide may be MnO₂ or (Mn_0.95Fe_0.05)₂O₃. Suitable chlorine sources include, but are not limited to, lithium perchlorate, lithium chloride, manganese chloride, iron chloride, cobalt chloride, and nickel chloride. These materials are mixed together and ground using conventional grinding methods. Suitable conventional grinding methods include, but are not limited to, using a mortar and pestle. This mixture is then calcined in Step S23 in a furnace at 600° C. for 2 hours. Alternatively, suitable calcination temperatures and times range from 350° C. to 800° C. (for 1 to 4 hours), from 400° C. to 600° C. (for 1.5 to 3 hours), or from 500° C. to 600° C. (for 2 to 2.5 hours).

In Step S24 of FIG. 2, the charge transfer catalyst salts and a chelating agent are dissolved in distilled or deionized water and nitric acid, and this solution is added to the calcined mixture. Suitable charge transfer catalyst salts include, but are not limited to, bismuth nitrate, arsenic nitrate, and antimony nitrate. Suitable chelating agents include, but are not limited to, glycine, cellulose, citric acid, a cellulose-citric acid mixture, and urea. Suitable volumetric quantities of nitric acid range from 5 vol % to 20 vol % in distilled or deionized water. In Step S25, the resultant mixture is heated to create a gel. Heating may be accomplished using a hot plate. In Step S26, the gel is heated further until auto ignition occurs. The resultant ash is ground and calcined in a furnace at 600° C. for 2 hours in Steps S27 and S28, respectively. A mortar and pestle may be used for grinding. Suitable alternative calcination temperatures and times range from 350° C. to 800° C. (for 1 to 4 hours), from 400° C. to 600° C. (for 1.5 to 3 hours), or from 500° C. to 600° C. (for 2 to 2.5 hours). In the final “B” and “O” site modified Li_xMn_2-yMe_yO_4-zCl_z material, where Me is Fe, Co, or Ni with a MO_b or MMn_aO_b charge transfer catalyst coating, x ranges from 0.05 to 1.9, 0.8 to 1.3, or 0.9 to 1.1; y ranges from 0.00 to 0.60, 0.005 to 0.3, or 0.03 to 0.3; and z ranges from 0.005 to 0.25, 0.005 to 0.05, or 0.015 to 0.035. In the MO_b or MMn_aO_b coating, X ranges from 0.5 to 25, 1 to 20, or 3 to 15. Regarding the charge transfer catalyst coating, a ranges from 0 to 10. Additionally, b ranges from 0 to 22, or b is greater than 0 but less than or equal to 22.

In an exemplary embodiment, the lithium source is lithium nitrate, the manganese source is manganese nitrate, the metal source is a Group VIII Period 4 element (Fe, Co, or Ni) nitrate, and the chlorine source is a chlorine-containing salt. These materials are mixed together in Step 21. Suitable alternative lithium sources include, but are not limited to, lithium carbonate, lithium hydroxide, and lithium chloride. Suitable alternative manganese sources include, but are not limited to, manganese chloride, manganese hydroxide, and manganese carbonate. Suitable chlorine-containing salts include, but not limited to, lithium chloride, manganese chloride, iron chloride, cobalt chloride, and nickel chloride. In this embodiment, a chelating agent is added to the mixture and the resulting mixture is dissolved in distilled or deionized water. Suitable chelating agents include, but are not limited to, glycine, cellulose, citric acid, a cellulose-citric acid mixture, and urea. In this embodiment, two additional steps occur before the grinding step: First, the solution is heated until the water fully evaporates and a gel is formed. Heating may be accomplished on a hot plate. Second, the gel is heated further until auto ignition occurs and forms an ash. The ash is collected and ground in Step S22. A mortar and pestle may be used for grinding. It is to be understood by one of ordinary skill in the art that grinding may be accomplished by other means. This mixture is then calcined in Step S23 in a furnace at 600° C. for 2 hours. Alternatively, suitable calcination temperatures and times range from 350° C. to 800° C. (for 1 to 4 hours), from 400° C. to 600° C. (for 1.5 to 3 hours), or from 500° C. to 600° C. (for 2 to 2.5 hours).

In Step S24 of FIG. 2, the resultant calcined mixture, a charge transfer catalyst salt, and a chelating agent are dissolved in distilled or deionized water and nitric acid to form a solution. Suitable charge transfer catalyst salts include, but are not limited to, bismuth nitrate, arsenic nitrate, and antimony nitrate. Suitable chelating agents include, but are not limited to, glycine, cellulose, citric acid, a cellulose-citric acid mixture, and urea. Suitable volumetric quantities of nitric acid range from 5 vol % to 20 vol % in distilled or deionized water. In Step S25, the resultant mixture created in Step S24 is heated to form a gel. Heating may be accomplished on a hot plate. In Step S26, the gel is heated further until auto ignition occurs. The resultant ash is ground and calcined in a furnace at 600° C. for 2 hours in Steps S27 and S28, respectively. Alternatively, suitable calcination temperatures and times range from 350° C. to 800° C. (for 1 to 4 hours), from 400° C. to 600° C. (for 1.5 to 3 hours), or from 500° C. to 600° C. (for 2 to 2.5 hours). In the final “B” and “O” site modified Li_xMn_2-yMe_yO_4-zCl_z material where Me is Fe, Co, or Ni with a MO_b or MMn_aO_b coating, x ranges from 0.05 to 1.9, 0.8 to 1.3, or 0.9 to 1.1; y ranges from 0.00 to 0.60, 0.005 to 0.3, or 0.03 to 0.3; and z ranges from 0.005 to 0.25, 0.005 to 0.05, or 0.015 to 0.035. In the MO_b or MMn_aO_b coating, X ranges from 0.5 to 25, 1 to 20, or 3 to 15. Regarding the MO_b or MMn_aO_b coating, a ranges from 0 to 10. Moreover, b ranges from 0 to 22, orb is greater than 0 but less than or equal to 22.

The exemplary process described above results in the formulation of a family of “B” and “O” site modified Li_xMn_2-yMe_yO_4-zCl_z, where Me is Fe, Co or Ni with X mol % MO_b or MMn_aO_b coating. The general formula for the lithium electrochemical cell cathode prepared is Li_xMn_2-yMe_yO_4-zCl_z with X mol % MO_b or MMn_aO_b coating, where M is iron, cobalt or nickel, and x 1 and proves to be reversible between 4.5 and 2.0 volts. This reversible region for x in a lithium electrochemical cell comprised of the present disclosure ranges from 0.05 to 1.9, y ranges from 0.0 to 0.6, and z ranges from 0.005 to 0.25.

FIGS. 3 and 4 show the X-ray diffraction pattern of an exemplary formulation mixture according to exemplary embodiments of the present disclosure compared to known reference standards. The figures show the final Li_xMn₂O_4-zCl_z with 15 mol % Bi of the form Bi₂Mn₄O₁₀ coating material according to the present disclosure. The bismuth to manganese ratio is 0.149, or approximately 15 mol %. Included in FIG. 4 is the standard data for intensity and location from the International Center for Diffraction Data for Bi₂Mn₄O₁₀ (JCPDS catalog number 027-0048) and LiMn₂O₄ spinel (JCPDS catalog number 018-0736). FIGS. 5 and 6 show the X-ray fluorescence (XRF) pattern for an exemplary formulation mixture of the present disclosure. Included in FIGS. 5 and 6 is the data describing the final Li_xMn₂O_4-zCl_z with 3 mol % and 15 mol % Bi material, respectively (which equates to bismuth to manganese ratios of 0.0379 and 0.149), as well as intensity and energy level for the system components. These components include the palladium X-ray source and silicon, sulfur, and phosphorus from the sample holder. XRF is performed on every sample for determining the mol % of M contained within the material.

FIG. 7 shows the thermogravimetric analysis results of Li_xMn₂O_4-zCl_z spinel with X mol % Bi added at Step S17 prior to calcination according to exemplary embodiments of the present disclosure. In the exemplary image shown in FIG. 7, the bismuth to manganese ratio is 0.135, or approximately 13 mol %. Between 30 and 120° C., the mass loss can be attributed to the dehydration of the physically absorbed water molecules. From 200 to 300° C., a mass loss is observed and can be attributed to the melting and denitration of remaining nitrates in the precursor via NO₂ evolution. In the 300 to 400° C. range, the mass loss could be due to residual glycine decomposition into CO₂, N₂, and H₂O in combination with formation of the spinel. Between 400 and 500° C., a slight mass increase occurs due to oxidation. Above 500° C., the mass loss is most likely due to chlorine evolution.

FIG. 8 shows a backscattered SEM image of the final Li_xMn₂O_4-zCl_z spinel with 15 mol % Bi coating according to an exemplary embodiment of the present disclosure. This image was taken with the following SEM settings: 5.0 kV, 6.1 mm×20.0 k SE(U,HA). The contrast is due to the Z scatter of the contained elements showing a majority gray structure with submicron second phase Bi₂Mn₄O₁₀ in a pale gray dispersed on the surface. In the exemplary image shown in FIG. 8, bismuth is the charge transfer catalyst coating on the modified lithium manganese-based AB₂O₄ spinel cathode material.

In order to evaluate the electrochemical properties of the present Li_xMn₂O_4-zCl_z or Li_xMn_2-yMe_yO_4-zCl_z, where Me is Fe, Co, or Ni with X mol % MO_b or MMn_aO_b coating in an electrochemical system, laboratory coin cells were fabricated using conventional methods described in detail below. Experimental cells may also be fabricated using other methods known in the art, incorporating the charge transfer catalyst coated Li_xMn₂O_4-zCl_z or the charge transfer catalyst coated Li_xMn_2-yMe_yO_4-zCl_z, where Me is Fe, Co, or Ni, lithium manganese-based AB₂O₄ spinel material described in the present disclosure. The experimental cells were composed of a lithium anode separated from a polytetrafluoroethylene (commercially available under the trade name TEFLON, manufactured by DuPont) bonded cathode with a nonwoven glass separator. Other suitable anode materials include, but are not limited to, lithium metal, lithium aluminum alloy, lithium silicon alloy, graphite and graphite derivatives, tin oxide, and lithium phosphate. The cathode was fabricated by combining Li_xMn_2-yMe_yO_4-zCl_z, carbon, and polytetrafluoroethylene in a 75:15:10 weight percent basis, respectively. Suitable conductive carbon materials include, but are not limited to, conductive carbon black (commercially available from various sources, including Cabot Corporation, under the trade name VULCAN XC72 or VULCAN XC72R), graphite, carbon nanofibers, and carbon nanoparticles (commercially available under the trade name PURE BLACK, manufactured by Superior Graphite Co.). Suitable binders include, but are not limited to, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), and latex. The cathode may contain by weight 40%-95% Li_xMn_2-yMe_yO_4-zCl_z with X mol % MO_b or MMn_aO_b (where X ranges from 0.5 to 25.0, 1 to 20, or 3 to 15), 1%-40% of conductive carbon, and 1%-20% binder.

The cathode mix was rolled to 0.06 cm and dried in a vacuum oven. The cathode mass was approximately 0.1 g. The cathode and 0.075 cm thick lithium foil was cut using a 1.58 cm diameter (1.96 cm²) hole punch. A 0.01 cm nonwoven glass separator was used for the separator and as a wick. The electrolyte used was 1 M LiPF₆ in proportional mixtures of dimethyl carbonate and ethylene carbonate. Other suitable electrolytes include, but are not limited to, lithium hexafluoroarsenate monohydrate (LiAsF₆·H₂O), lithium perchlorate (LiClO₄), lithium tetrafluoroborate (LiBF₄), and lithium triflate (c). The cells were cycled with an ARBIN Model MSTAT4 Battery Test System. The charge profile consisted of a constant current charge at 1.0 or 2.0 mA to 4.5 volts. The cells were discharged at 1.0, 2.0, 4.0, 6.0, 8.0, or 16.0 mA to 2.0, 2.25 or 3.0 or 3.5 volts. Additionally, pulse tests were performed upon discharge at 8.0 mA for 1 minute followed by a 3 minute rest. A rest period of 15 minutes between cycles allowed for the cells to equilibrate. Prior to cycling, cell impedance was recorded with a Solartron, SI1260 Frequency Response Analyzer with a Solartron, SI1287 Electrochemical Interface using Scribner Associates, Inc., ZPlot and ZView software. The data is used as a quality control tool and for comparative use between variant chemistries.

The data shows stable Li_xMn₂O_4-zCl_z or Li_xMn_2-yMe_yO_4-zCl_z with X mol % MO_b or MMn_aO_b (where M is Bi, As, or Sb) charge transfer catalyst coating was formulated, fabricated, and characterized as a positive electrode suitable for lithium and lithium ion rechargeable electrochemical cells and batteries. The general formula for the present spinel material is Li_xMn_2-yMe_yO_4-zCl_z with X mol % MO_b or MMn_aO_b where Me is Fe, Co, or Ni; M is Bi, As, or Sb; and X ranges from 0.5 to 25.0, 1 to 20, or 3 to 15. Moreover, x ranges from 0.05 to 1.9, 0.8 to 1.3, or 0.9 to 1.1; y ranges from 0.00 to 0.60, 0.005 to 0.3, or 0.03 to 0.3; and z ranges from 0.005 to 0.25, 0.005 to 0.05, or 0.015 to 0.035. In addition, a ranges from 0 to 10. Moreover, b ranges from 0 to 22, or b is greater than 0 but less than or equal to 22.

The rate capability of the Li_xMn₂O_4-zCl_z or Li_xMn_2-yMe_yO_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coated cathode material is demonstrated with greater than 90% of specific discharge capacity through 200 cycles from 4.5 to 3.0 Vat 8 mA/cm² (120 mA/g, with a C-rate of approximately 1C) and greater than 75% of specific discharge capacity through 140 cycles at 16 mA/cm² (240 mA/g, approximately 2C rate). The specific capacity for the Li_xMn₂O_4-zCl_z or Li_xMn_2-yMe_yO_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode material ranged from 50 to 80 mAh/g when coupled with lithium and cycled between 4.5 and 3.0 volts. This is less than conventional lithium manganese-based AB₂O₄ spinel materials fabricated over a 48 to 72-hour time span due to the addition of the very heavy charge transfer catalyst materials. The specific capacity for the Li_xMn₂O_4-zCl_z or Li_xMn_2-yMe_yO_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode material was 130 to 170 mAh/g when coupled with lithium and cycled between 4.5 and 2.0 volts. In the MO_b or MMn_aO_b coating, X ranges from 0.5 to 25, 1 to 20, or 3 to 15.

FIGS. 9-11 show discharge capacity and galvanostatic (charge/discharge) plots for lithium electrochemical cells fabricated with Li_xMn₂O_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode material, synthesized using the method described in the present disclosure. In the exemplary plots shown in FIGS. 9-11, bismuth is the charge transfer catalyst coating on the modified lithium manganese-based AB₂O₄ spinel cathode material. The bismuth to manganese ratio in FIGS. 9-11 is 0.0379, or approximately 3 mol %.

FIGS. 9 and 10 show exemplary discharge capacities through 500 and 600 cycles, respectively, with select charge and discharge curves displayed in FIG. 11 for lithium electrochemical cells fabricated with Li_xMn₂O_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode material, synthesized using the method described in the present disclosure. All cycles were cycled between 4.5 V to 3.0 V. Cycles 1-12 were charged and discharged at 1.1 mA/cm², cycles 13-20 were charged at 2 mA/cm² and discharged at 8 mA/cm², cycles 21-30 were charged and discharged at 2 mA/cm², cycles 31-500 were charged at 2 mA/cm² and discharged at 8 mA/cm², cycles 501-550 were charged at 2 mA/cm² and pulse discharged at 8 mA/cm² for 1 minute and rested for 3 minutes, and cycles 551-600 were charged and discharged at 2 mA/cm². Good capacity retention is demonstrated at extended cycling at a high rate, 8 mA/cm² (1C rate, 104 mA/g). FIG. 11 shows after extended cycling at a high rate, 90% of the discharge capacity can be recovered with pulse discharging at 8 mA/cm² for 1 minute and rest for 3 minutes at cycle 505, which is equivalent to the 2 mA/cm² discharge at cycle 565, as compared with the early cycling at the same 2 mA/cm² rate at cycle 25.

FIG. 12 shows the discharge capacity per cycle comparing two chemistries, one being Li_xMn₂O₄ synthesized using Steps S21-S23 without “B” or “O”-site modification before the addition of the charge transfer catalyst, and Li_xMn₂O_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode material, synthesized using the method described in the present disclosure. In the exemplary plots shown in FIG. 12, bismuth is the charge transfer catalyst coating on the modified lithium manganese-based AB₂O₄ spinel cathode material. The bismuth to manganese ratio is 0.0379, or approximately 3 mol %. All cycles were cycled between 4.5 V to 3.0 V. The Li_xMn₂O₄ synthesized using Steps S21-S23 without “B” or “O”-site modification before the addition of the charge transfer catalyst was cycled at 1 mA/cm² for cycles 1-126, cycles 127-146 were charged at 2 mA/cm² and discharged at 8 mA/cm², cycles 147-166 were charged at 2 mA/cm² and discharged at 4 mA/cm², cycles 167-206 were charged at 2 mA/cm² and discharged at 6 mA/cm², and cycles 207-226 were charged and discharged at 2 mA/cm². The Li_xMn₂O_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode material was charged and discharged at 1.1 mA/cm² for cycles 1-12, cycles 13-20 were charged at 2 mA/cm² and discharged at 8 mA/cm², cycles 21-30 were charged and discharged at 2 mA/cm², cycles 31-225 were charged at 2 mA/cm² and discharged at 8 mA/cm². The high rate capability with the addition of the charge transfer catalyst coating is demonstrated in FIG. 12 by the very small loss in discharge capacity from lower rates (1-2 mA/cm²) to the higher 8 mA/cm² rate for the Li_xMn₂O_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode material versus a greater than 10% difference in discharge capacity for the Li_xMn₂O₄ synthesized using Steps S21-S23 without “B” or “O”-site modification before the addition of the charge transfer catalyst material.

FIG. 13 is a differential capacity graph of cycles 130 through 140 illustrating exemplary cycle life traces for three separate lithium cells, one being Li_xMn₂O_4-zCl_z synthesized using Steps S11-S13 before the addition of the charge transfer catalyst, one being Li_xMn₂O₄ synthesized using Steps S21-S23 without “B” or “O” site modification before the addition of the charge transfer catalyst, and Li_xMn₂O_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode material, synthesized using the method described in the present disclosure. In the exemplary plot shown in FIG. 13, bismuth is the charge transfer catalyst coating on the modified lithium manganese-based AB₂O₄ spinel cathode material. The bismuth to manganese ratio is 0.03, or approximately 3 mol %. Differential capacity traces provide information regarding the underlying thermodynamics and kinetics of an electrochemical cell. The differential capacity data uses galvanostatic control of the electrochemical system being tested, and plots the capacity increase (charge) or decrease (discharge) as a function of potential. During cycles 130-140, all cells were cycled between 4.5 V to 3.0 V with a charge rate of 2 mA/cm² and discharge rate of 8 mA/cm². This figure shows that only with the addition of the charge transfer catalyst coating is the electrochemistry more reversible (corresponding peaks are closer together) and the electrochemical activity is completed faster, almost entirely before 3.5 V upon discharge as shown by the narrower peaks.

FIG. 14 is a bar graph of the percent of discharge capacity at cycle 150 discharged from 4.5 to 3.0 V at 8 mA/cm² versus cycle 5 discharged at 1 (9 mol % Bi) mA/cm² or 2 mA/cm² (no Bi, 3 mol % Bi, 9 mol % Bi with 6% Co, and 15 mol % Bi) for five separate chemistries, one being Li_xMn₂O_4-zCl_z synthesized using Steps S11-S13 before the addition of the charge transfer catalyst, and four different Li_xMn_2-yMe_yO_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode materials, synthesized using the method described in the present disclosure. In the exemplary plot shown in FIG. 14, bismuth is the charge transfer catalyst coating on the modified lithium manganese-based AB₂O₄ spinel cathode material and one embodiment includes Me=Co, where y=0.06. The bismuth to manganese ratio is 0.0379, 0.0959, 0.0848, 0.149 or approximately 3, 9, 8, and 15 mol %. The high rate capability is demonstrated in all four charge transfer catalyst embodiments showing approximately 80% capacity retention or greater for an 8 mA/cm² discharge at extended cycling compared to less than 70% capacity retention for the same synthesis only without the addition of the charge transfer coating described in Steps S14-18 of FIG. 1 and Steps S24-28 of FIG. 2.

FIG. 15 is a bar graph of the percent of discharge capacity at cycle 140 discharged from 4.5 to 3.0 V at 16 mA/cm² versus cycle 5 discharged 2 mA/cm² for four separate embodiments, one being Li_xMn₂O_4-zCl_z synthesized using Steps S11-S13 before the addition of the charge transfer catalyst, and three different Li_xMn_2-yMe_yO_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode materials, synthesized using the method described in the present disclosure. In the exemplary plot shown in FIG. 15, bismuth is the charge transfer catalyst coating on the modified lithium manganese-based AB₂O₄ spinel cathode material and in one embodiment, Me is cobalt and y=0.06. The bismuth to manganese ratio is 0.0379, 0.0848, 0.149 or approximately 3, 9, and 15 mol %. The high rate capability is demonstrated in all three charge transfer catalyst chemistries showing approximately 52-75% capacity retention for a 16 mA/cm² discharge at extended cycling compared to less than 40% capacity retention for the same synthesis only without the addition of the charge transfer coating described in Steps S14-18 of FIG. 1 and Steps S24-28 of FIG. 2.

FIGS. 16-19 show discharge capacity per cycle and the galvanostatic charge/discharge cycle plots for 3 exemplary electrochemical cells with Li_xMn_2-yMe_yO_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode material, synthesized using the method described in the present disclosure. In the exemplary plots shown in FIGS. 16-19, bismuth is the charge transfer catalyst coating on the modified lithium manganese-based AB₂O₄ spinel cathode material and cobalt is the “B” site modifier where y=0.06. The bismuth to manganese ratio is 0.0848, or approximately 9 mol %. The cells were cycled from 4.5V to 3.0V. Cell 1 was charged and discharged at 1 mA/cm² for cycles 1-10, cycles 11-20 were charged at 2 mA/cm² and discharged at 4 mA/cm², cycles 21-140 were charged at 4 mA/cm² and discharged at 8 mA/cm², and cycles 141-150 were charged and discharged at 2 mA/cm². Cell 2 was charged and discharged at 2 mA/cm² for cycles 1-10, cycles 11-140 were charged at 2 mA/cm² and discharged at 8 mA/cm², and cycles 141-150 were charged and discharged at 2 mA/cm². Cell 3 was charged and discharged at 2 mA/cm² for cycles 1-10, cycles 11-20 were charged at 2 mA/cm² and discharged at 8 mA/cm², cycles 21-140 were charged at 2 mA/cm² and discharged at 16 mA/cm², and cycles 141-150 were charged and discharged at 2 mA/cm². In FIG. 16, cell 3 shows excellent capacity retention at the very high 16 mA/cm² discharge rate (2C, 234 mA/g) over cycles 21-140. This comports with the 8 mA/cm² discharge rate capacities of the other two cells across the same cycle region. In FIGS. 17-19, the charge and discharge curves for the 2 mA/cm² cycling at cycle 145 and cycle 5 are nearly identical after extended cycling at high rates for all three cells. FIG. 19 shows how quickly the electrochemistry can be performed at the very high 16 mA/cm² discharge rate capacity, with essentially no damage to the crystal before and after the high rate cycling in the charge transfer catalyst coated AB₂O₄ spinel material.

FIGS. 20-22 show the galvanostatic charge/discharge cycle plots for 3 exemplary electrochemical cells with Li_xMn₂O_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode material, synthesized using the method described in the present disclosure. In the exemplary plots shown in FIGS. 20-22, bismuth is the charge transfer catalyst coating on the modified lithium manganese-based AB₂O₄ spinel cathode material. The bismuth to manganese ratio is 0.149, or approximately 15 mol %. All cells were cycled from 4.5 to 3.0 V. Cell 4 was charged and discharged at 1 mA/cm² for cycles 1-10, cycles 11-19 were charged at 2 mA/cm² and discharged at 4 mA/cm², cycles 20-39 were charged at 2 mA/cm² and discharged at 16 mA/cm², cycles 40-221 were charged at 2 mA/cm² and discharged at 8 mA/cm², and cycles 222-231 were charged and discharged at 1 mA/cm². Cell 5 was charged and discharged at 1 mA/cm² for cycles 1-10, cycles 11-21 were charged at 2 mA/cm² and discharged at 4 mA/cm², cycles 22-31 were charged at 2 mA/cm² and discharged at 8 mA/cm², cycles 32-241 were charged at 4 mA/cm² and discharged at 8 mA/cm², and cycles 242-251 were charged and discharged at 1 mA/cm². Cell 6 was charged and discharged at 1 mA/cm² for cycles 1-10, cycles 11-22 were charged at 2 mA/cm² and discharged at 8 mA/cm², cycles 23-242 were charged at 2 mA/cm² and discharged at 16 mA/cm², and cycles 243-252 were charged and discharged at 1 mA/cm². FIGS. 20-22 demonstrate reasonable capacity retention at 1 mA/cm² after greater than 200 cycles at high rates (16 and 8 mA/cm²) due to the addition of the charge transfer catalyst coating on the AB₂O₄ spinel material.

FIGS. 23 and 24 show galvanostatic charge and discharge curves for an exemplary electrochemical cell with Li_xMn₂O_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode material, synthesized using the method described in the present disclosure. In these figures, bismuth is the charge transfer catalyst coating on the modified lithium manganese-based AB₂O₄ spinel cathode material. The bismuth to manganese ratio is 0.0959, or approximately 9 mol %. The cell was cycled from 4.5 V to 3.0 V from cycles 1 through 150. The charge and discharge rate for cycles 1-10 was 2 mA/cm², cycles 11-150 were charged at 2 mA/cm² and discharged at 8 mA/cm². For cycles 151 to 162, the charge and discharge rates were 2 mA/cm², but the discharge potential oscillated back and forth from 3.0 V to 2.25 V to access the second lithium insertion. In FIG. 23, the high rate capability is demonstrated by negligible loss of capacity between the 2 mA/cm² discharges at cycles 155 and 5 after the long cycling at elevated discharge rate 8 mA/cm². In FIG. 24, the deep discharge to 2.25 V is shown achieving twice the capacity achieved in the 4.5 to 3.0 V discharge. This figure demonstrates that the charge transfer catalyst coated spinel material exhibits deep discharge capability as a result of the “O” site chlorine modifications through the continued charge and discharge in cycle 153, and the cycles up to 155, as shown in FIG. 23.

FIGS. 25 and 26 are charge/discharge hysteresis and electrochemical impedance spectroscopy (EIS) plots comparing two chemistries, one with Li_xMn₂O_4-zCl_z synthesized using Steps S11-S13 before the addition of the charge transfer catalyst, and another with Li_xMn₂O_4-zCl_z with X mol % MO_b or MMn_aO_b charge transfer catalyst coating cathode material, synthesized using the method described in the present disclosure. In these figures, bismuth is the charge transfer catalyst coating on the modified lithium manganese-based AB₂O₄ spinel cathode material. The bismuth to manganese ratio is 0.149, or approximately 15 mol %. In FIG. 25, the first four cycles after the forming cycle (2-5) from 4.5 to 3.0 V with a charge/discharge rate of 2 mA/cm² are displayed against a normalized capacity for comparison purposes. The material containing the bismuth charge transfer catalyst coating shows a far smaller hysteresis in cycling, indicating faster kinetics during electrochemical cycling. FIG. 26 is the electrochemical impedance measured at 3.6 V of open circuit voltage immediately following cell fabrication. This figure supports the enhanced kinetic properties of the bismuth charge transfer coating by demonstrating a far smaller charge transfer resistance upon cell fabrication.

The above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments which fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

Claims

1. A method of preparing a coated homogeneously dispersed li_xMn_2-yMe_yO_4-zCl_z spinel cathode material, the method comprising:

mixing a lithium source, a chlorine source, and a manganese source to form a first mixture;

calcining the first mixture to produce a homogeneously dispersed li_xMn_2-yMe_yO_4-zCl_z spinel cathode material;

mixing the homogeneously dispersed li_xMn_2-yMe_yO_4-zCl_z spinel cathode material, a charge transfer catalyst salt, and a chelating agent to produce a second mixture;

heating the second mixture to produce a gel;

igniting the gel to form an ash; and

calcining the ash to produce the coated homogeneously dispersed li_xMn_2-yMe_yO_4-zCl_z spinel cathode material comprising a charge transfer catalyst coating,

wherein the charged transfer catalyst coating comprises a compound that is selected from a group consisting of mo_b and MMn_aO_b,

wherein M is selected from a group consisting of bismuth, arsenic, and antimony,

wherein Me is selected from a group consisting of iron, cobalt, and nickel, and

wherein x ranges from 0.05 to 1.9, y ranges from 0.005 to 0.3, and z ranges from 0.005 to 0.25.

2. The method according to claim 1, wherein the lithium source is selected from a group consisting of lithium carbonate, lithium hydroxide, lithium oxide, lithium peroxide, and lithium nitrate,

wherein the chlorine source is selected from a group consisting of lithium perchlorate, lithium chloride, manganese chloride, iron chloride, cobalt chloride, and nickel chloride, and

wherein the manganese source is selected from the group consisting of manganese oxide, (MnMe_f)O₂, (MnMe_f)₂O₃, (MnMe_f)₃O₄, (MnMe_f)O, and manganese nitrate.

3. The method according to claim 1, wherein a ranges from 0 to 10.

4. The method according to claim 1, wherein b is greater than 0 or equal to or less than 22.

5. The method according to claim 1, further comprising:

heating the first mixture to form an intermediate gel, and

igniting the intermediate gel,

wherein the first mixing step further comprises mixing a group VIII Period 4 element source and the chelating agent.

6. The method according to claim 1, wherein the calcining steps comprise calcining the first mixture at 350° C. to 800° C. for 1 to 4 hours and calcining the ash at 350° C. to 800° C. for 1 to 4 hours.

7. The method according to claim 1, wherein the charge transfer catalyst salt is a compound selected from a group consisting of bismuth nitrate, arsenic nitrate, and antimony nitrate, and wherein the chelating agent is a compound selected from a group consisting of glycine, cellulose, citric acid, a cellulose-citric acid mixture, and urea.

8. The method according to claim 5, wherein the group VIII Period 4 element source is selected from a group consisting of iron nitrate, cobalt nitrate, and nickel nitrate.